The invention relates to a valuable document comprising at least one security element which in a marking area comprises a marking layer that is applied to a carrier body and comprises electroluminescent pigments. It furthermore relates to a method for producing such a valuable document.
For protection against forgeries or copies, valuable documents or security documents such as bank notes, identity cards or chip cards, for example, are provided with so-called security features or security elements which are intended to reliably rule out inter alia the possibility of forgery by making color copies, for example in the case of valuable documents in paper form. The security elements may in this case be designed in particular as optically variable elements, such as holograms or interference layer elements for example, which, when viewed, give different color impressions depending on the viewing angle, but are not transferred to the copy during the copying process. The optically variable elements may in this case also be applied in the form of pigments, so-called OVI pigments, which in particular allows processing by means of printing technology. However, such security elements cannot or can only with difficulty be read or evaluated by machine, so that automated security checking of the respective valuable documents is possible only to a limited extent and with a high level of technical complexity.
However, DE 197 08 543 discloses a valuable document which in particular is also suitable for automated evaluation of its security elements. To this end, the valuable document comprises, as the security element, in a marking area, a marking layer with added electroluminescent pigments which is applied to a carrier body, for example the banknote paper. When this security element is checked or authenticated, the marking layer comprising the electroluminescent pigments is exposed to an alternating electric field via a suitably designed test device, in a contactless manner. The alternating electric field excites the electroluminescent pigments contained in the marking layer to bring them to the point of luminescence, and this can be recorded directly or indirectly in a suitable receiver. Particularly in combination with the corresponding test device, this type of valuable document is thus particularly suitable for automated and thus particularly reliable evaluation with only limited technical complexity.
However, it has been found that relatively high electric fields are necessary for reliable excitation of the electroluminescent pigments in such a valuable document. Depending on the integration of the electroluminescent pigments in the surrounding matrix, it is even conceivable that the field strengths required for excitation lie above the breakdown field strengths of the matrix, so that excitation cannot take place or can take place only under much more difficult conditions. The use of electroluminescent pigments (favorable on account of their ability for automated evaluation) in a security element of a valuable document is thus possible only to a limited extent.
The object of the invention is to provide a valuable document of the type mentioned above which allows the use of electroluminescent pigments in the security element for a particularly large number of use and environmental conditions. Moreover, a method which is particularly suitable for producing such a valuable document is also provided.